Jewel bearings for printer heads and the like

ABSTRACT

Jewel bearings for printer head assemblies and the like which are especially adapted for use in high speed printers of the dotmatrix type. A die-cast member is provided with a rear wall for mounting driving solenoids each having recipricating print wires extending from the rear wall toward the front wall thereof so as to be positioned to impact a paper document. Guide members are provided for maintaining the position of the print wires between the front and rear walls while enabling reciprocating action thereof. The guide members are provided with jewel bearings to maintain the alignment of the print wires while at the same time providing minimal wear even after long continuous and repeated use. The driving solenoids may also be fitted with jewel bearings. A front wall jewel bearing assembly accurately alignes the free ends of the print wires for reciprocating movement to reduce wear of the wires and to provide low frictional engagement with the inked ribbon.

United States Patent 1 Howard m1 3,802,543 [4 1 Apr. 9, 19.7.4

[ JEWEL BEARINGS FOR PRINTER HEADS AND THE LIKE [75] Inventor:

[73] Assignee: Centronics Data Computer Corp.,

Hudson, N.H.

[22] Filed: Sept. 13, 1971 [21] App]. No.: 179,627

52 US. Cl 197/1 R [51], Int. Cl B41j 3/04 [58] Field of Search 197/1; 308/3, 4, 36

[56] References Cited UNITED STATES PATENTS 3,298,753 1/1967 Eaton 308/36 3,679,273 7/1972 Cupler.... 308/36 3,333,667 8/1967 Nordin 197/1 3,217,640 11/1965 Bradshaw 197/1 X 3,672,482 6/1972 Brumbaugh et a1. 197/1 3,603,442 9/1971 Ward 197/1 3,627,096 12/1971 Finnegan.... 197 1 2,129,065 9/1938 Loop 197/1 R 2,632,386 3/1953 Hyland.... 197/1 R X 3,108,673 10/1963 Green 197/1 R 3,333,667 8/1967 Nordin 197/1 R 3,467,232 9/1969 Paige 197/1 R 3,584,575 6/1971 Distl 197/1 R X 3,603,442 9/1971 Ward; 197/1 R FOREIGN PATENTS OR APPLICATIONS 364,273 9/1962 Switzerland 197/43 Robert Howard, Roslyn, N.Y.

Primary Examiner-Robert E. Bagvvill Assistant Examiner-R. T, Rader Attorney, Agent, 0r Firm-Ostrolenk, Faber, Gerb & Soffen 5 7 ABSTRACT Jewel bearings for printer head assemblies and the like enabling reciprocating action thereof. The guide members are provided with jewel bearings to maintain the alignment of the print wires while at the same time providing minimal wear even after long continuous and repeated use. The driving solenoids may also be fitted with jewel bearings. A front wall jewel bearing assembly accurately alignes the free ends of the print wires for reciprocating movement to reduce wear of the wires and to provide low frictional engagement with the inked ribbon.

3 CIaims,-14 Drawing Figures JEWEL BEARINGS FOR PRINTER HEADS AND THE LIKE The present invention relates to low friction bearing means and more particularly to jewel bearings for guidingslender reciprocating wires which may for example be used in high speed printers so as to maintain the orientation of the reciprocating wires throughout their use while at the same time significantly reducing wear.

BACKGROUND OF THE INVENTION known in the prior art. A dot-matrix printer which has been proven to be quite successful isdescribed in copending application Ser. No. 37,815 filed May 15, 1970 and assigned to the assignee of the present invention. The aforesaid application describes a printer head assembly for such dot-matrix printers which employes seven reciprocating print wires whose forward most free ends are typically arranged along an imaginary vertical line at the print end of the one-piece die-cast member. Each of the print wires are reciprocated by an associated solenoid member mounted upon the rear wall of the diecast member whereby upon selective energization of the solenoids, the print wires are caused to impact a paper document (preferably through an inker ribbon). By providing a driving mechanism to move the print wire assembly across the paper document it is possible to print any character number or symbol upon thepaper document. Typically the print wire assembly is advanced across the paper document and at five discrete closely spaced positions the print wire solenoids are selectively energized to form a seven by five dot-matrix which is capable of representing any desired character, number or symbol.

The print head assembly is typically moved at a substantially constant rate of speed across the paper document necessitating the use of high speed solenoids capable of driving their associated print wires to impact the paper document and reset within a very short span of time so as to be ready to print the next vertical column of dots. 1n a printer of the type described hereinabove, the printing speed of a full line is usually of the order of more than 132 characters per second, Assuming five columns make up each character, the print wires must therefore be capable of operating (i.e. impacting and resetting) at least 665 times per second. The print wires which move a distance of approximately 0.15 inches of a necessity must be capable of being rapidly accelerated to provide the desired impact force and be capable of being rapidly accelerated toward the reset position. Due to the rapid acceleration of the print wires (in both the printing and resetting direction) a whipping" effect is experienced by the print wires causing the wires to move in a transverse direction and thereby frictionally engage the print wire guide means. This effect is especially pronounced near the forward and rearward ends of the print wires so as to cause undue wearing of both the print wires and the BRIEF DESCRIPTION OF THE INVENTION.

The present invention is characterized by providing jewel bearing assemblies for use in dot matrix printers and the like in which guide means are provided for accurately positioning the print wires near their forward and rearward ends whileat the same time substantially reducing wear of both print wires and guide means to yield a print wire assembly having an extremely long and useful operating life. I

The present invention, in one preferred embodiment, is comprised of a one-piece die-cast housing having a rear wall for preferably threadedly mounting the forward threaded ends of a plurality of solenoid drivers clustered together upon the rear wall in a rather compact fashion. The solenoid drivers are each mechanically coupled to an associated print wire. The print wires extend through the rear'wall and toward the front wall and are arranged to converge together at the front wall of the die-cast housing where they are aligned along an imaginary straight line and arranged in very closely spaced fashion. A jewel bearing mounted in the front wall of the housing effectively provides an extremely low friction guiding means for the forward free ends of the print wires as well as eliminating any frictional engagement between the forward ends of the print wires and the paper document (or inked ribbon) which may otherwise occur even when the print wires are in the retracted position due to the close spacing between the front face of the printer head housing and the paper document.

The portions of the print wires between the forward and rearward ends extend between the forward and rearward walls of the die-cast member and are gradually curved over this length. To maintain their curvature, at least a pair of retainer'plates are provided at spaced intervals within the diecast housing. The retainer plates are provided with jewel bearing which are fixedly secured within associated apertures provided in ings, with the interior surface of the opening being a smoothcurve so as to reduce friction. The narrower throat reduces the area of each jewel bearing whick makes surface contact with its associated reciprocating print wire, thus minimizing the amount of engagement therebetween and significantly reducing the wear of both the jewel bearing and the print wires.v

The barriers may each alternatively be comprised of an intermediate plate provided with openings for receiving each jewel bearing member with the intermediate plate and the jewel bearing members being sandwiched between a pair of retainer plates preferable spot welded to the intermediate plate. Each of the retainer plates are provided with openings having diameters aligned with the jewel bearing members and being smaller than the outer most diameter of the jewel bearin'g member so as to fixedly secure each jewel bearing member within the opening provided for it in the intermediate plate and between the pair of retainer plates.

As -another alternative embodiment the retainer plates may be provided with openingsfor receiving hollow elongated guide tubes, each of which is adapted for receiving a reciprocating print wire. The ends of the guide tubes may each be provided with a jewel bearing which may be fitted within an enlarged opening provided at the ends of each guide tube with the marginal lip of the opening being swaged so as to retain the jewel bearing within the guide tube. Alternatively, jewel bearings may be fitted against the ends of the guide tubes and be retained thereat by a cap means which telescopes over the end of the guide tube so as to retain the jewel bearing in position.

As still another alternative embodiment, the retainer assemblies may be comprised of a channel shaped retainer plate for receiving and fixedly securing one end of a guide tube. A second retainer plate arranged a spaced distance from the channel shapped guide plate is fitted with a jewel bearing in each of its openings which are retained therein by any of the techniques described hereinabove so as to provide a jewel bearing for each of the print wires near the forward and rearward ends thereof.

In a like manner the solenoid assembly may be similarly fitted with jewel bearings either at the forward end thereof or at both forward and rearward ends so as to minimize wearing of the print wire within the solenoid.

The front jewel which maintains the print wires in closely spaced fashion along an imaginary straight line is preferably formed of a pair of jewel members each provided with semi-circular grooves which are aligned so as to define circularv shaped apertures for receiving the print wires. The jewels are accurately aligned relative' to one another preferably within a jig assembly and are joined together by channel shaped members secured thereto by means of a suitable epoxy. Alternatively the channel shaped members may be replaced by a one piece rectangular frame into which the jewel bearing members are fitted and, after accurate alignment, are epoxied to the frame member.

The jewel bearing members described hereinabove significantly reduce wearing of the print wires and the guide members (if used) as well as the jewel bearing members themselves, while maintaining the desired curvature of the print wires during operation thereof so as to provide a print wire assembly having an extremely long useful operating life even after repeated high speed use.

It is therefore one object of ,the present invention to provide novel jewel bearing arrangements for use in print wire assemblies and the like.

Another object of the present invention is to providea novel jewel bearing assembly for use in print wire aligning barrier plates to maintain the spacing and curvature of a plurality of print wires even during operation thereof while at the same time significantly reducing wear even after long repeated use at high operating speeds. 7

Another object of the present invention is to provide guide means fitted with jewel bearings for use in print wire assemblies and the like so as to provide a print wire assembly having a minimum amount of wear.

BRIEF DESCRIPTION OF THE FIGURES.

These as well as other objects of the present invention will become apparent when reading the accompanying description and drawings in which:

FIG. 1 is a top plan view of a printer head assembly embodying the principals of the present invention.

FIG. 1a is side elevational view of the embodiment of FIG. 1 partially sectionalized to facilitate an understanding of the apparatus.

FIG. 2 is an elevational view of a barrier plate assembly which may be employed as a substitute for those shown in FIGS. 1 and la.

FIG. 2a is an enlarged sectional view of a portion of the assembly of FIG. 2 looking in the direction of Arrows A-A.

FIG. 2b is an elevational view of the intermediate plate member of the assembly of FIGS. 2 and 2a.

FIGS. 20 and 2d show an alternative arrangement for the embodiments of'FIGS. 2 through 2b.

FIG. 3 shows still another preferred embodiment of the present invention employing guide wires having jewel bearings. I

FIGS. 4a and 4b show detailed sectional views of one free end of the guide wires in which two alternative arra'ngements for mounting jewel bearings are shown.

FIGS. 5 and 7 show an arrangement of a solenoid employed in the embodiment of FIG. 1, for example, which is fitted with jewel bearings.

FIGS. 6a and 6b show two alternative arrangements for the jewel bearing members provided in the forward wall of the print wire assembly die-cast ho'using.

DETAILED DESCRIPTION OF THE FIGURES FIGS. la and lb show a printer head assembly 10 comprised of a one piece die-cast housing member 11 having a pair of flanges 12a and 12b which extend to the sides of the housing as well as extending below the housing and which are provided with openings 13 for receiving suitable fastening members to secure housing 11 upon a movable carriage assembly (not shown).

The rear end of member 11 is provided with an upwardly projecting wall 14 having a plurality of tapped openings 15 whose longitudinal axes are aligned so as to be substantially perpendicular to their associated exterior surfaces 142, 14b, 14c and 14d shown in FIGS. 1 and 1a. The openings are aligned so that their longitudinal axes intersect at a remote point, which point lies on an imaginary line which is coincident with the central axis of opening 15.

Each of the openings is tapped to threadedly engage the threaded collar 17 of a print solenoid 18. Each of the solenoid assemblies are similarly provided with threaded collars for threadedly engaging an associated one of the tapped aperatures 15 (or 15). Each solenoid has a slender solenoid wire 19 (or 19) projecting outwardly through an opening provided at the forward end of each threaded collar 17, which print wires extend from the forward end of each solenoid assembly and through the hollow interior of the housing 11 so as to extend substantially to the forward end thereof in a manner to be more fully described.

Die-cast member 11 is further provided with a rear mounting portion 20 comprised of inwardly directed projections 21 and 22 formed integrally with the side walls 11a and 11b of die-cast member 11. Each of the projections is provided with a narrow slot 21a and 22a respectively, for receiving a substantially thin planar sheet 23 provided with .a plurality of openings, each adapted to receive a toroidal shaped jewel bearing 24. Sheet 23 is inserted within narrow slots 21a and 22a so that its bottom edge rests against the bottom surface 11c of die-cast member 11 (see FIG. 1a). An epoxy is provided at to retain planar'sheet 23 in position. Each of the jewel bearings 24 are likewise epoxied as shown for example at 26 so as to ridgidly maintain each of the jewel bearings in position within the their associated openings provided in plate 23.

Die cast member 11 is further provided with a forward mounting portion 27 comprised of first andsecond projections 28 and 29 extending inwardly from side walls 11a and 11b and provided with narrow slots 28a and 29a respectively for receiving a thin planar sheet 30 whose opposite marginal edges are fitted Within slots 28a and 29a. The bottom edge of sheet 30 rests against the base portion 11d of die case member 11 and is epoxied as shown at 31 to retain the sheet in position.

Sheet or plate 30 is similarly provided with a plurality of openings each receiving a jewel member 24 which members are epoxied as shown at 32 so as to retain the jewel bearings within their associated oepnings in plate 30.

The print wires 19 and 19) extend forwardly from their associated solenoids sothat each of the print wires passes through the central opening provided in each of the toroidal shaped jewels, with the forward free ends of the print wires additionally being mounted to reciprocate within a final jewel bearingassembly 34 which, as was previously described, is positioned in very close proximity to a paper document and associated inked ribbon so as to minimize frictionalengagement with the inked ribbon (not shown for purposes of simplicity) and to prevent the print wires from engaging the inked ribbon when in the retracted position (ie the reset position).

It can be seen from FIGS. 1 and 1a that the print wires (with the exception of printwire 19') are curved in the plane of both Figures. Due to the extremely high speed operation of the print wires, which wires are rapidly accelerated in the forward direction to impact the inked ribbon and paper document and are further rapidly accelerated in the rearward direction to return to the reset position, the print wires undergo a whipping effect whereby the portions of the print wires near their forward and rearward ends experience movement or whipping in the direction transverse to the direction of movement. The jewel bearings serve to restrain their associated print wires from experiencing any movement other than-in the forward and rearward direction as well as providing an extremely low friction engagement with the print wires so as to substantially reduce wear of the print wires near their forward and rearward ends and thus provide a structure having an extremely long and useful operating life evan after repeated high speed use.

An alternative jewel bearing mounting arrangement which may be used in place of that shown in FIGS. 1 and la is shown in FIGS. 2, 2a and 2b. Since the structure of the alternative barrier plate assembly is substantially identical for both the forward and rearward assemblies 27 and 20 shown in FIGS. 1 and 1a, only one such assembly will be described herein for purposes of simplicity, it being understood'that the only distinction of jewel 24 and are slightly greater than the inner diam between the two assemblies resides in the relative placement of the openings receiving the print wires and in the shape and outer contour of the barrier plate assemblies. v

The barrier plate assembly 40 of FIG. 2 is comprised of an intermediate plate 41 which is shown independently of the other components in FIG. 2b and is further comprised of a pair of retainer plates 42 and 43 of substantially identical size and configuration. The, intermediate plate 41 is provided with a plurality of openings 41a each of which is adapted to receive a jewel member 24 as is shown best in FIG. 2a. The openings 41a have a diameter substantially equal to the outer diameter of each jewel member. The retainer plates 42 and 43 are each provided with a plurality of openings 42a and 43a respectively, with the centers of these openings being aligned with one another as Well as being aligned with the centers of. the openings 41a and the'central axes of the jewels 24. FIG. 2a shows the arrangement wherein the centers of openings 42a and 43a provided in plates 42 and 43 and the center of opening 41a and the longitudinal axes of toroidal shape jewel 24-all lie on a common axes represented by phantom line 45. The diameters of the openings 42a and 43a are substantially smaller than the'outer diameter eter of jewel 24. To assemble the structure of FIGS. 2

through 2b, the toridal shaped jewels are first inserted into the openings 41a in intermediate plate 41. Plates 42 and 43 are then positioned on opposite sides of plate 41 in a manner shown best in FIGS. 2 and 2a with all of the holes being in alignment. Preferable, the intermediate plate 41 is provided with a pair of positioning holes 41b and the plates 42 and 43 are provided with similar positioning holes (only the positioning holes 42b being shown in plate 42 for purposes of simplicity) whereby accurate alignment as between .the three plates is exactly determined. The plates are then joined together preferably by spot welding at the points 46.

It can be seen that the width of plate 41 is substantially greater than the width of plates 42 and 43. The

vertical marginal edges ofplate 41 are thus inserted within the narrow slots 28a and 29a provided in the forward projections 28 and 29 described hereinabove in connection with FIGS. 1 and 1a. The assembly 40 may be epoxied as shown at 31 in FIG; la to retain the assembly within the die-cast housing 11.

The rearward mounting assembly 20 is substantially identical to that described hereinabove with the exception that the retainer plates and intermediate plates would be of a larger size and would be. provided with holes at different relative positions so as to maintain the gradual and smooth curvature of theprint wires along their entire length.

FIGS. 2c and 2d show a slightly modified arrangement from that depicted in FIGS. 2 through 2b wherein intermediate plate 41' is provided with a substantially rectangular shaped opening 41a which is fitted with a sheet 24' formed of the same material as jewels 24 which is drilled or otherwise machined so as to provide openings 24a. Sheet 41 is then sandwiched between.

retainer plates 42 and 43 in a manner similar to that described hereinabove, again preferably with the use of the alignment positioning holes so as to sandwich plate 41 and jewel sheet 24, between plates 42 and 43 in the manner shown best in FIG. 20. If desired, the positioning holes 24b may be drilled withing the jewel s'he'et 24 to assure alignment of the jewel sheet relative to the openings provided in retainer plates 42 and 43.

As an obvious alternative to the arrangement shown in FIGS. 1 and 1a the plurality of openings provided'in plates 23 and 30 may be replaced by a rectangular shaped opening (or an opening of any other suitable configuration) into which a jewel sheet may be fitted and retained by a suitable epoxy. The jewel sheets would then be drilled or otherwise machined so as to,

provide openings at the appropriate positions.

FIG. 3 shows a view substaintially similar to that shown in FIG. 1 wherein the barrier plates 30 and 23 are provided with suitable openings for receiving hollow tube guides 47, each of which extend between the front wall lle and the rear wall 14 of die-cast member 11. The tube guides are secured within associated openings provided in plates 23 and 30 preferably by means of an epoxy provided for example at 48. Although not shown for purposes of simplicity, one such tube guide is provided for each print wire 19.

Each of the tube guides are provided at their free ends with a jewel bearing arrangement which may take the form of that shown in either FIG. 4a or 4b.

FIG. 4a shows one end of a tube guide 47 having a central opening 47a. The outermost interior portion of central opening 47a is drilled or otherwise machined so as to provide a widened diameter portion 47b. A jewel bearing 24 is fitted within the enlarged diameter portion as shown, preferably in a press fitted manner. The extreme end 47c of the tube is then swaged over the right hand end of jewel 24 so as to firmly retain the jewel in position within the tube guide. It should be understood that either end or both ends of the tube guides may be provided with jewel bearings in the manner shown in FIG. 4a.

FIG. 4b shows another alternative arrangement for affixing jewels to one or both ends of the tube guides wherein a jewel 24 is fitted within the interior of a cap 48 adapted to telescope over the end of the tube guide 47 in the manner shown. The cylindrical portion 48a of the cap is preferably force fitted over the associated end of the tube guide 47 andmay be retained thereon by spot welding, by the use of an epoxy, or any other suitable material or securement technique. The cap 48 is provided with an opening 48b whose diameter is narrower than the outer diameter of the toroidal shaped jewel 24 so as to permit the free and unimpeded passage of a print wire through the central opening 24a of jewel 24 while at the same time securing the jewel to the end of the tube guide.

Still another alternative embodiment of the invention is shown in FIG. 1 which may be modified so as to employ the jewel bearings shown therein together with tube guides. In this embodiment, a channel shaped plate 50 having, mounting surfaces 50a and 50b, is positioned in close proximity to plate 30 with the mounting surfaces 50a and 50b preferably being spot welded to plate 30. The central portion 50c of plate 50 is provided with openings for receiving and securing the forward ends of tube guides 47 in the manner shown. As can be seen, the forwardmost ends of tube guides47 lie a slightly spaced distance away from the rearward ends of their associated jewels 24 thus providing separate securement means for the tube guides and the jewel members.

FIG. shows a sectional veiw of a solenoid 18 comprising a one-piece shell member 50 whose right-hand portion is substantially cylindrical in shape and is threaded at 17. A fastening nut 51 (note also FIGS. 1 and la) threadedly engages threaded collar 17 for the purpose of tightening and locking the solenoid to rear wall 14 of the die cast member 11 once the solenoid is accurately positioned relative to the die cast member. The left-hand portion of shell 50 is also cylindrical in shape and has a cylindrical wall 53 which defines a hollow annular shaped interior region 54 which houses solenoid coil 55. The central core portion 52 has a centrally located opening 56 for slidably receiving print wire 19 which is secured to the left-hand end of cylindrical shaped armature member 57 and which passes through a narrow diameter opening 56 to a wider ope'ning 56a and a still wider diameter opening 56b provided in shell 50. A tubular shaped wire guide 58 surrounds a portion of print wire 19 in the manner shown. The guide is preferably force fitted within the portion 560 of the elongated opening provided in shell 50. A suitable dry powdered lubricant is preferably provided within the interior surface of wire guide 58 to minimize wear during reciprocating movement of the print wire.

The armature member 57 which is formed of a permanent magnet material is secured to a disc-shaped member 61 formed of a springy or resilient metallic material by means of a rivet 62. An end cap 66 retains the spring member between the interior surface of the end cap and the spacer member 65 in the manner shown. End cap 66 is tapped as shown at 67 so as to engage the threaded portion 68 of shell 50.

A jewel member 24 is fitted at the forward end of wire guide 58, which jewel member may be secured thereto by either of the arrangements as shown in FIGS. 4a and 4b. If desired, the rear end 58a of print wire guide 58 may similarly be fitted with a jewel member in a fashion similar to that described hereinabove.

FIGS. 6a and 6b show two alternative arrangements for the jewel bearing provided at the front wall lle. Considering FIG. 6a, for example, the jewel assembly 34 is comprised of a pair of jewel sheets 34a and 34b each provided with a plurality of'semi-circular grooves 34c and 34d, respectively. The jewel members are aligned with their adjacent straight edges 34c and 34f, respectively, engaging one another and with the semicircular portions arranged so that they cooperate to form circular shaped apertures. Preferably a jig means (not shown for purposes of simplicity) may be employed to maintain accurate alignment between the two plates. After alignment, a pair of C-shaped clips Cl and C2 are positioned along the upper and lower edges respectively of the assy. Whereas the figure indicates the arms of the clips asbeing wider than the jewel sheets, it should be understood that the clips are preferably arranged in very closely fitting fashion to the jewel sheets. An epoxy is provided between the engaging surfaces of the clips in the jewel sheets so as to firmly maintain a position the jewel sheets relative to one another.

The embodiment 34 of FIGS. 6b differs from that shown in FIG. 6a in that the C-shaped clips Cl and C2 have been replaced by a rectangular shaped frame F. The assembly arrangement is substantially the same as that described hereinabove wherein an epoxy is provided within the region 34g between the outer edges of the jewel sheets 34a and 34b and the interior edges of the frame F. Once the assembly 34 (or 34) has been v 9 completed, it may then be simply and readily epoxied into; position withinthe slot provided within the front wall lle of the one-piece die cast housing.

FIG. 7 shows a detailed sectional view of one preferred embodiment of a jewel 24. The jewel 24 is of toroidal shape and is provided with a central opening 24a for receiving a print wire. The opening 24a has a narrow throat portion 24b arranged at a location intermediate the ends of the opening with the interior surface being gradually curved as shown so as to provide a smooth and gradual transition between the narrow throat portion 24b and the widened ends of the opening 24a. This arrangement provides minimul surface contact between the jewel bearing member and its associated print wire. This arrangement is preferred whether toroidal shaped jewel members are utilized or whether jewel sheets of the type shown by sheet 24' in FIG. 20 is employed so as to minimize both frictional engagement and wearing.

It can be seen from the foregoing description that the present inventionprovides novel jewel bearing assemblies for use in print solenoids and printer heads wherein lateral movement of the print wires is minimized while at the same time reducing wear of both the print wire and the jewels even after long high speed repeated use.

What is claimed is:

l. A movable unitary printer head assembly for use in impact printers of the dot matrix type comprising:

a housing having front and rear walls joined by a pair of side walls and a floor defining a hollow interior;

a pluralityof print wire driving means secured to said rear walls; j each of said driving means including a print wire extending through said housing rear wall with their forward free ends extending through said hollow interior and terminating adjacent said front wall; spacing means secured within said front wall for maintaining the free ends of said print wires in a predetermined alignment; first and second print wire positioning and guiding assemblies mounted in a stationary fashion at spaced intervals within said housing and adjacent said front and rear walls respectively;

jewel bearing means secured to said guiding assemblies and having openings each adapted to receive an associated print wire therethrough for substantially restraining transverse movement of the print I said sheet means being comprised of first and second planar jewel sheets each having a print wire spacing edge confronting the print wire spacing edge of the other sheet;

.each of said edges being provided with a plurality of semi-circular grooves arranged at spaced intervals along said edges; i

the semi-circular grooves of said edges being aligned to define circular openings for receiving and guiding the free ends of said print wires;

metal frame means embracing said sheets to maintain their alignment and means for securing said sheets to said frame.

2. The apparatus of claim 1 wherein the opening in each of said jewel members has a narrow throat portion intermediate the ends of said opening with the opening gradually increasing in diameter on opposite sides of said throat portion to minimize sliding contact between said jewel members and said print wires.

3. The apparatus of claim 1 wherein said frame means comprises first and second C-shaped clips embracing the upper and lower ends of said sheet to maintain their alignment and means for securing said sheets to said clips. 

1. A movable unitary printer head assembly for use in impact printers of the dot matrix type comprising: a housing having front and rear walls joined by a pair of side walls and a floor defining a hollow interior; a plurality of print wire driving means secured to said rear walls; each of said driving means including a print wire extending through said housing rear wall with their forward free ends extending through said hollow interior and terminating adjacent said front wall; spacing means secured within said front wall for maintaining the free ends of said print wires in a predetermined alignment; first and second print wire positioning and guiding assemblies mounted in a stationary fashion at spaced intervals within said housing and adjacent said front and rear walls respectively; jewel bearing means secured to said guiding assemblies and having openings each adapted to receive an associated print wire therethrough for substantially restraining transverse mOvement of the print wires and maintaining a plurality of said print wires in a predetermined pattern to retain the gradual curvature assumed by the print wires between said front and rear walls while significantly reducing wear of said wires even after long and repeated high-speed operation and use; said jewel bearing means comprising a plurality of toroidal shaped jewel members each secured in an associated one of said openings and receiving a print wire therethrough said spacing means comprising a planar multi-apertured jewel sheet means forming a jewel bearing assembly; said sheet means being comprised of first and second planar jewel sheets each having a print wire spacing edge confronting the print wire spacing edge of the other sheet; each of said edges being provided with a plurality of semicircular grooves arranged at spaced intervals along said edges; the semi-circular grooves of said edges being aligned to define circular openings for receiving and guiding the free ends of said print wires; metal frame means embracing said sheets to maintain their alignment and means for securing said sheets to said frame.
 2. The apparatus of claim 1 wherein the opening in each of said jewel members has a narrow throat portion intermediate the ends of said opening with the opening gradually increasing in diameter on opposite sides of said throat portion to minimize sliding contact between said jewel members and said print wires.
 3. The apparatus of claim 1 wherein said frame means comprises first and second C-shaped clips embracing the upper and lower ends of said sheet to maintain their alignment and means for securing said sheets to said clips. 